The two riders broke away with less than 23km to go in the 197km race that includes more than 50km of Tuscany's white gravel roads. The pair worked well together to hold-off an elite chase group including Valverde, former winner Fabian Cancellara (Trek Factory Racing), Roman Kreuziger (Tinkoff-Saxo), and Damiano Cunego (Lampre-Merida).

Kwiatkowski's win was a true team effort. After flatting inside the race's final 50km, the Polish champion was paced back to the pack by teammates, leaving him well-positioned for the finale. As the leading group began to dwindle following the race's longest gravel sector, Omega Pharma team drove the front of the pack, setting-up Matteo Trentin for a solo attack that put other teams on the defensive.

Once the Italian was reeled back in, Sagan counter-attacked and Kwiatkowski was quick to respond. Inside the final kilometer, he had no trouble dropping the Slovak champion on the steep pitches of the climb to the finish.

"When I came around the final corner to the finish line in Piazza del Campo, it was absolutely beautiful," Kwiatkowski said. "I did recon yesterday of the finish in Siena, and it was amazing then as well. But with fans and spectators around, it's even better. It's something special."

The victory is the biggest of the 23-year-old's career and his fifth of the season for Omega Pharma—Quick-Step, an impressive haul for a rider many consider to be a future Tour de France contender.